WO2014050579A1 - Electrode active material for capacitor, and capacitor using said electrode active material - Google Patents

Abstract

An electrode active material for a capacitor, the electrode active material containing a porous carbon material, wherein: the BET specific surface area of the porous carbon material is 800 m²/g or more; the X-ray diffraction image of the porous carbon material obtained by using Cukα rays has a peak (P_k) at 2θ= 40 to 50 degrees; P_k contains a peak (P_d111) component belonging to the (111) plane of a diamond crystal; and when the X-ray diffraction image has a peak (P_G002) belonging to the (002) plane of graphite, the ratio of the intensity (I_G002) of P_G002 relative to the intensity (I_k) of P_k is 3.0 or less when I_G002/I_k.

Description

Electrode active material for capacitor and capacitor using the same

The present invention relates to an electrode active material for a capacitor containing a porous carbon material, and further relates to a capacitor using such an electrode active material for a capacitor, in particular, an electric double layer capacitor (EDLC) or a lithium ion capacitor (LIC).

Non-Patent Document 1 describes that carbon materials having various structures from amorphous to graphite can be produced by chlorinating metal carbides. According to Non-Patent Document 1, the structure and pore size distribution of the generated carbon material vary depending on the type of metal carbide and the reaction conditions.

On the other hand, Patent Document 1 describes that a porous carbon material obtained by chlorination of metal carbide is used as an electrode active material of an electric double layer capacitor. More specifically, it is described that TiC is reacted with chlorine at 900 ° C. to 1000 ° C. to produce a porous carbon material having nano-level pores.

JP-T-2004-513529

As described above, as a method of generating a porous carbon material, a method of reacting a metal carbide with chlorine gas is known, and the use of the generated porous carbon material as an electrode material of a capacitor is also being studied. However, the structure of the porous carbon material obtained by such a chlorination reaction is various, and it cannot necessarily be said that it has an optimal structure as an electrode active material for capacitors. Therefore, it is desired to control the microstructure of the porous carbon material so that the suitability as an electrode active material for capacitors can be increased as much as possible.

One aspect of the present invention includes a porous carbon material, the BET specific surface area of the porous carbon material is 800 m ² / g or more, and an X-ray diffraction image of the porous carbon material by Cukα rays is 2θ = It has a peak: P _k at 40 ° to 50 °, and P _k contains a component of a peak: P _d111 attributed to the (111) plane of the diamond crystal. 002) If the peak attributed to the plane: P _G002 , the _ratio of the intensity of P _G002 : the intensity of I _G002 to the intensity of P _k : I _k (I _G002 / I _k ) is 3.0 or less. The present invention relates to an electrode active material.

The porous carbon material is considered to have a crystal structure similar to diamond because P _k contains a peak component attributed to the (111) plane of the diamond crystal. Here, it is known that diamond crystals generally do not have electron conductivity. Therefore, it is predicted that the electron conductivity of the porous carbon material is reduced. However, the porous carbon material has excellent electronic conductivity despite having a crystal structure similar to diamond. Further, its electronic conductivity is more isotropic than a general carbon material such as graphite. Such excellent isotropy is considered to be derived from a crystal structure similar to diamond. Furthermore, the porous carbon material is excellent in mechanical strength, and even when it has a large specific surface area of 800 m ² / g or more, the strength required as a capacitor material can be sufficiently maintained. Such excellent mechanical strength is considered to be derived from a crystal structure similar to diamond.

The position of P _k is preferably on the higher angle side than 2θ = 43 degrees. This is because if the position of P _k is higher than 2θ = 43 degrees, the porous carbon material is considered to contain more diamond component.

The intensity of P _k is preferably at least 3 times the intensity of the peak at 2θ = 10 degrees, more preferably at least 5 times. This is because, when such a peak intensity ratio is satisfied, the pores of the porous carbon material are sufficiently developed, which is preferable in terms of capacitance characteristics as a carbon material for capacitors.

The crystallite size determined from the half width of P _k is preferably 1.0 nm to 10.0 nm. By setting the crystallite size to 10.0 nm or less, it is considered that the original characteristics of the diamond crystal are suppressed and more excellent electron conductivity is exhibited. Moreover, it is thought that more excellent mechanical strength and isotropic electron conduction can be obtained by setting the crystallite size to 1.0 nm or more.

In the volume-based pore diameter distribution of the porous carbon material, the cumulative volume of pores having a pore diameter of 1 nm or less is preferably 80% or more of the total pore volume. This significantly increases the specific surface area of the porous carbon material, which is more advantageous for the formation of the space charge layer.

When the porous carbon material is produced by a predetermined production method, the porous carbon material has a specific surface area of 800 m ² / g or more without performing an activation treatment with an alkali or an activation treatment with water vapor. Accordingly, since impurities derived from the activation treatment are not mixed, the content of the alkali metal element in the porous carbon material can be 0 ppm to 400 ppm. The hydrogen content contained in the porous carbon material can be 0 ppm to 100 ppm. By using a porous carbon material having an alkali metal element content of 0 ppm to 400 ppm and a hydrogen content of 0 ppm to 100 ppm, side reactions during charging and discharging of the capacitor are remarkably suppressed. .

Another aspect of the present invention includes a first electrode, a second electrode, a separator interposed between the first electrode and the second electrode, and an electrolyte solution. The first electrode and the second electrode At least one of them relates to a capacitor containing the capacitor electrode active material. Since such a capacitor includes a porous carbon material having excellent electron conductivity, excellent isotropic electron conduction, and excellent mechanical strength as an active material, it has low electrical resistance and excellent cycle characteristics. .

The electrolytic solution of the capacitor has lithium ions (Li ⁺ ), tetraethylammonium ions (TEA ⁺ ), triethylmonomethylammonium ions (TEMA ⁺ ), 1-ethyl-3-methylimidazolium ions (EMI ⁺ ) and N as cations. -Containing at least one selected from the group consisting of -methyl-N-propylpyrrolidinium ion (MPPY ⁺ ), and as anions, hexafluorophosphate ion (PF ₆ ⁻ ), perchlorate ion (ClO ₄ ⁻ ) , Tetrafluoroborate ion (BF ₄ ⁻ ), lithium bis (oxalate) borate ion (BC ₄ O ₈ ⁻ ), bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ⁻ ), bis (trifluoromethanesulfonyl) imide ion _{(N (SO 2 CF 3)} 2 -), bis (Pentafuru B ethanesulfonyl) imide ion _{(N (SO 2 C 2 F} 5) 2 -), trifluoromethanesulfonate ion (CF ₃ SO ₃ ^-) preferably contains at least one selected from the group consisting of. Such an electrolytic solution is excellent in ion conductivity and electrode permeability, and improves the characteristics of the capacitor.

When the capacitor is a lithium ion capacitor comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive nonaqueous electrolyte, the nonaqueous electrolyte is A non-aqueous solvent and a lithium salt that dissolves in the non-aqueous solvent, and the non-aqueous solvent is an ionic liquid or an organic solvent. The ionic liquid contains as a cation at least one selected from the group consisting of 1-ethyl-3-methylimidazolium ion (EMI ⁺ ) and N-methyl-N-propylpyrrolidinium ion (MPPY ⁺ ), As anions, bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ⁻ ), bis (trifluoromethanesulfonyl) imide ion (N (SO ₂ CF ₃ ) ₂ ⁻ , bis (pentafluoroethanesulfonyl) imide ion (N ( SO ₂ C ₂ F ₅ ) ₂ ⁻ ) and trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ), and preferably contains at least one selected from the group consisting of: Excellent ion conductivity and permeability to electrodes.

By using the capacitor electrode active material of the present invention, a capacitor having low resistance and excellent cycle characteristics can be provided.

2 is an X-ray diffraction image (waveform X) having a peak attributed to the (111) plane of a diamond crystal, which is an example of a porous carbon material produced by reacting silicon carbide (SiC) with chlorine gas. It is an electron micrograph of the porous carbon material, and is a view showing a carbon microcrystal having a layer structure or an onion structure. X-ray diffraction image (waveform Y) of a porous carbon material produced by reacting titanium carbide (TiC) with chlorine gas, and porous produced by reacting aluminum carbide (Al ₄ C ₃ ) with chlorine gas It is a figure which shows the X-ray-diffraction image (waveform Z) of a carbon material in contrast with the waveform X. FIG. It is a figure which shows the relationship between the heating temperature when making silicon carbide react with chlorine gas, and the weight decreasing rate of silicon carbide. It is a figure which shows the relationship between the heating temperature when making silicon carbide react with chlorine gas, and the specific surface area (t-plot by BET method and Langmuir method) of the produced | generated porous carbon material. It is a figure which shows the relationship between the heating temperature when making silicon carbide react with chlorine gas, and the pore diameter distribution of the porous carbon material to produce | generate. It is a figure which shows the relationship between the total pore volume of the porous carbon material produced | generated by making silicon carbide react with chlorine gas, and a BET specific surface area. It is a contrast figure of the X-ray-diffraction image of the porous carbon material produced | generated by making silicon carbide and chlorine gas react at 1100 degreeC, 1200 degreeC, and 1400 degreeC. It is sectional drawing which shows the structure of an example of a capacitor. It is a flowchart which shows the flow of each process of an example of the manufacturing method of a porous carbon material. It is a figure which shows roughly the structure of the carbon production | generation apparatus which produces | generates a porous carbon material. It is a figure which simplifies and shows the structure of the zinc reduction apparatus used in the process of reduce | restoring the metal chloride produced | generated when producing | generating a porous carbon material. It is a figure which shows roughly the structure of the carbide | carbonized_material production | generation apparatus which produces | generates a metal carbide. FIG. 4 is an enlarged view of a portion of 2θ = 40 degrees to 48 degrees in FIG.

[Electrode active material for capacitors]
First, the electrode active material for capacitors will be described.
The capacitor electrode active material of the present invention includes a porous carbon material. However, the X-ray diffraction image of the porous carbon material by Cukα rays has a peak: P _d111 attributed to the (111) plane of the diamond crystal. Such a porous carbon material is considered to have at least a part of a crystal structure similar to diamond, and is more excellent in isotropy of electron conduction than, for example, graphite. Therefore, such a porous carbon material has a low electrical resistance and can provide a capacitor with excellent current collection. By having a diamond structure, the potential window can be made wider than that of graphite or amorphous carbon, and the effect of suppressing deterioration due to the high voltage of the electrode can be considered. In addition, a porous carbon material having an X-ray diffraction image of _Pd111 can maintain a mechanical strength for a long period of time even if the specific surface area is very large, so that a capacitor having high capacity and excellent cycle characteristics can be obtained. Obtainable.

More specifically, the X-ray diffraction image of the porous carbon material has a peak: P _k at 2θ = 40 degrees to 50 degrees, and P _k is a peak attributed to the (111) plane of the diamond crystal: _Contains P _d111 component. At this time, all components of P _k may be components belonging to the (111) plane of the diamond crystal. That is, a relationship of P _k = P _d111 may be _satisfied .

When the porous carbon material comprises graphite component, 2 [Theta] = 40 to 50 degrees, i.e. in a range that overlaps with P _d111, peaks attributed to the (010) plane of the graphite: P _G010 appears. In this case, at 2θ = 20 ° to 30 °, a peak belonging to the (002) plane of graphite: _PG002 is simultaneously observed. At this time, the position of P _k may be 2θ <43 degrees.

From the above, when the X-ray diffraction image by the Cukα ray has a peak attributed to the (002) plane of graphite: P _G002 , P _k of 2θ = 40 ° to 50 ° is synthesized by P _G010 and P _d111. Peak. Even in such a case, if the ratio (I _G002 / I _k ) of P _G002 intensity: I _G002 intensity to P _k intensity: I _k is 3.0 or less, I _k is very _{high with} respect to I _G002 . _Therefore , P _k includes at least a component of P _d111 .

I _G002 / I _k is preferably 3.0 or less, and more preferably 2.5 or less. When such a peak intensity ratio is satisfied, even if the porous carbon material contains a graphite component, properties of ordinary graphite are hardly expressed, and properties based on a crystal structure similar to diamond are strongly expressed. The intensity (I) of each peak is the height from the base line of the X-ray diffraction image. Here, the baseline is a signal having a background noise level. For example, the baseline near 2θ = 44 degrees in FIG. 1 is obtained by drawing a straight line between the intensity of 2θ = 35 degrees and the intensity of 2θ = 55 degrees. Since the baseline cannot be drawn at 2θ = 10 degrees, the height of the baseline is set to zero and the peak intensity is set to the intensity of X-ray diffraction.

By the way, the position of the peak attributed to the (002) plane of graphite is 2θ≈42.7 degrees, while the position of the peak attributed to the (111) plane of diamond is 2θ≈43.9 degrees. From this, it is considered that the component belonging to the (111) plane of diamond increases as the position of P _k becomes higher. Therefore, if the position 2θ of P _k is higher than 43 degrees, it is considered that the porous carbon material contains more diamond component.

FIG. 1 shows an X-ray diffraction image of an example of a porous carbon material having P _d111 . In FIG. 1, there is a broad peak P _k attributed to the (111) plane of the diamond crystal at 2θ = 40 ° to 50 °. The angle position at which the peak P _k appears almost overlaps with the position at which the peak of the (010) plane of graphite appears, but when graphite is present, it belongs to the (002) plane of graphite at 2θ = 20 degrees to 30 degrees. Peak: _PG002 is also observed at the same time. In FIG. 1, since _PG002 is not observed at 2θ = 20 ° to 30 ° and the position of P _k is 2θ = 43.8 °, the broad peak at 2θ = 40 ° to 50 ° is a diamond crystal. It can be seen that this is the peak P _d111 attributed to the (111) plane. Here, the position 2θ of P _k is an average value of two angles indicating a half value of the peak intensity (intensity top value).

In FIG. 1, the intensity I _{10 at} the diffraction angle 2θ = 10 degrees is about 10 times the peak intensity I _k of 2θ = 40 degrees to 50 degrees. Since the diffraction angle 2θ = 10 degrees represents a structure of 0.8 nm to 0.9 nm, it indicates the porosity of the carbon material. It is considered that the larger the diffraction intensity at this angle, the more pores are formed. The ratio of I ₁₀ to I _k (I ₁₀ / I _k1 ) is preferably 3.0 or more, and more preferably 5.0 or more. When such a peak intensity ratio is satisfied, the pores of the porous carbon material are sufficiently developed, which is preferable in terms of capacitance characteristics as a carbon material for capacitors.

Note that it is not synonymous that the peak P _d111 attributed to the (111) plane of the diamond crystal is confirmed and that the porous carbon material contains the diamond crystal. However, the presence of the peak P _d111 indicates at least the existence of a crystal structure similar to diamond.

The size of a crystallite (that is, a crystallite constituting a crystal similar to diamond) obtained from the half width of P _k is preferably, for example, 1.0 nm to 10.0 nm. The structure of the crystallite can be confirmed by an electron microscope of a cross section of the porous carbon material. The larger the crystallite, the stronger the properties similar to the diamond of the porous carbon material, and the smaller the specific surface area. Accordingly, the crystallite size is preferably 1.0 nm to 5.0 nm, and more preferably 1.0 nm to 3.0 nm.

Here, FIG. 2 shows an electron micrograph of an example of a porous carbon material having an X-ray diffraction image of Cdα rays having _Pd111 . In FIG. 2, the presence of carbon microcrystals having a layer structure or an onion structure can be confirmed. The particle diameter of the carbon microcrystal is about 2 nm. Since the porous carbon material has onion-structured carbon microcrystals as shown in FIG. 2, it is considered that the porous carbon material strongly develops properties similar to diamond. Therefore, although details are not clear, it is presumed that onion-structured carbon microcrystals belong to crystals similar to diamond. Thus, the porous carbon material is not completely amorphous and contains carbon microcrystals having a size of less than 10 nm.

In the volume-based pore size distribution of the porous carbon material, the cumulative volume of pores having a pore size of 1 nm or less is preferably 80% or more of the total pore volume, and more preferably 90% or more. . In this way, most of the pores of the porous carbon material are micropores of 1 nm or less, and the proportion of mesopores (pore diameter 2 nm to 50 nm) and macropores (pore diameter greater than 50 nm) is small. The specific surface area of the material becomes very large, and the proportion of the area where the space charge layer is formed becomes large. Therefore, a capacitor electrode having a large capacitance can be obtained.

The porous carbon material preferably has few impurities. This is because impurities cause internal short circuit of the capacitor, deterioration of cycle characteristics, increase of internal pressure due to gas generation, and the like. Examples of impurities that can be contained in the capacitor electrode active material include alkali metal elements, surface functional groups, and transition metal elements.

Alkali metal elements cause side reactions at the time of charging, which causes the cycle characteristics of the capacitor to deteriorate. Therefore, it is desirable that the porous carbon material does not contain an alkali metal element. Even when the alkali metal element is contained as an impurity, the content (mass) of the alkali metal element contained in the porous carbon material is preferably 400 ppm or less, more preferably 100 ppm or less, and 10 ppm or less. It is particularly preferred. Examples of alkali metal elements that can be included as impurities include lithium, sodium, potassium, cesium, and the like.

The surface functional group is a functional group that can exist on the surface of the porous carbon material. Such a functional group is usually a hydroxyl group, a carboxyl group, an alkyl group or the like, and contains a hydrogen atom. The surface functional group tends to cause a side reaction with the electrolytic solution in the capacitor. When a side reaction occurs, gas is generated in the capacitor, which causes a reduction in the cycle characteristics of the capacitor. Therefore, the hydrogen content (mass) contained in the porous carbon material is preferably 0 ppm to 100 ppm, and more preferably 50 ppm or less.

Since the transition metal element can cause an internal short circuit of the capacitor, it is desirable that the porous carbon material does not contain the transition metal element. The transition metal element can be contained in the raw material (for example, metal carbide) of the porous carbon material, but can be reduced to a sufficiently low concentration by controlling the conditions for generating the porous carbon material. The content (mass) of the transition metal element contained in the porous carbon material is preferably 100 ppm or less, and more preferably 10 ppm or less.

BET specific surface area of the porous carbon material, for example, 800 m ² / g may be at least, but from the viewpoint of obtaining a capacitor electrode of a high capacity, preferably at least 1000 m ² / g, more preferably at least 1100 m ² / g 1200 m ² / g or more is more preferable, and 1300 m ² / g or more is particularly preferable. BET specific surface area of the porous carbon material, for example 2500 m ² / g but not more than, 2000 m ² / g or less are common, not more than 1800 m ² / g, it is easy to more production. These upper and lower limits can be arbitrarily combined. That is, a preferable range of the BET specific surface area of the porous carbon material can be, for example, 1000 m ² / g to 2000 m ² / g, or 1100 m ² / g to 1800 m ² / g.

The porous carbon material having the above properties is, for example, a metal carbide having an average particle size of 0.1 μm to 100 μm, more preferably a metal carbide having an average particle size of 2 μm to 40 μm in an atmosphere containing chlorine gas. It can produce | generate by heating at 150 degreeC or more. Here, the average particle size is a particle size (D50) at which the cumulative volume becomes 50% in the volume-based particle size distribution. Hereinafter, the same applies to other materials. By using a powdered or porous metal carbide having an average particle diameter in such a range, a porous carbon material can be efficiently generated from the metal carbide. Further, the time required for producing the porous carbon material can be shortened. In addition, a porous body means the state which the particle | grains which comprise powder couple | bonded by aggregation and sintering.

When the metal carbide is reacted with chlorine gas, a porous carbon material and a metal chloride are generated. At this time, for example, silicon carbide (SiC) or titanium carbide (TiC) is selected as the metal carbide, and the heating temperature is set to 1100 ° C. or higher, preferably 1200 ° C. or higher, so that an X-ray diffraction image by CuKα rays can be obtained. A porous carbon material having _d111 is obtained. In addition, since the specific surface area of the produced | generated porous carbon material tends to reduce when heating temperature becomes high too much, heating temperature is 1500 degrees C or less, and 1400 degrees C or less is more preferable.

As described above, the porous carbon material generated by heating the metal carbide at the predetermined temperature in an atmosphere containing chlorine gas has a total volume of pores having a pore diameter of 1 nm or less as described above. 80% or more, and further has a sharp pore size distribution of 90% or more. Further, since the specific surface area is large, it is advantageous for forming the space charge layer. Furthermore, since the metal carbide used as a raw material itself is a material that hardly contains impurities, the produced porous carbon material has high purity, and the content of impurities is extremely small. Therefore, a porous carbon material having an alkali metal element content of 10 ppm or less, a hydrogen content of 50 ppm or less, and a transition metal element content of 10 ppm or less can be easily obtained.

As the metal carbide to be reacted with chlorine gas, it is preferable to use at least one selected from the group consisting of SiC and TiC because the generated porous carbon material tends to exhibit properties similar to diamond. Among these, the use of SiC makes it possible to obtain a porous carbon material that has smaller properties as graphite and is more excellent in isotropy of electron conduction.

FIG. 1 referred to above is an X-ray diffraction image of a porous carbon material produced by reacting SiC with chlorine gas at 1100 ° C., and FIG. 2 is a transmission electron of a cross section of the porous carbon material. It is a microscope (TEM) photograph. In FIG. 1, no peaks attributed to graphite are observed.

In addition, the peak seen in the vicinity of 2θ = 22 degrees in FIG. 1 is attributed to crystal, and the peak seen in the vicinity of 2θ = 26 degrees is attributed to cristobalite. These are derived from silica contained as impurities in SiC. However, crystal and cristobalite are stable in the capacitor and do not cause side reactions. Therefore, the necessity to limit these contents is very low. Further, when silica is used as a raw material for SiC, silica only remains in SiC, and silica is not necessarily contained in SiC.

On the other hand, FIG. 3 shows an X-ray diffraction image (waveform Y) of a porous carbon material produced by reacting TiC with chlorine gas at 1000 ° C., and Al ₄ C ₃ produced by reacting chlorine gas with 1000 ° C. The X-ray diffraction image (waveform Z) of the porous carbon material thus obtained is shown so that it can be compared with the X-ray diffraction image (waveform X) of FIG.

From FIG. 3, when Al ₄ C ₃ is used as the metal carbide, a broad peak at 2θ = 40 ° to 50 °: P _kz is observed, but 2θ = 20 ° to 30 ° A sharp peak is observed. A relatively sharp peak at 2θ = 20 ° to 30 ° is a peak attributed to the (002) plane of graphite: _PG002 . Then, the intensity of the P _G002: intensity of P _kz of I _G002: ratio _{I kz (I G002 / I kz} ) is 4.4. In this case, _since the strength of I _G002 is extremely large, it is considered that P _kz is practically attributed to the (010) plane of graphite. Moreover, even if P _kz contains a slight amount of the P _d111 component attributed to the (111) plane of the diamond crystal, properties derived from a crystal structure similar to diamond are hardly obtained.

Next, when TiC is used as the metal carbide, a broad peak: P _ky is observed at 2θ = 40 ° to 50 °, and it belongs to the (002) plane of graphite at 2θ = 20 ° to 30 °. Broad peak: _PG002 is observed. Here, a P _G002 is broad, the intensity of the P _G002: P _ky intensity of I _G002: since the ratio _{I ky (I G002 / I ky} ) is 2.7, the properties of the graphite can be suppressed ing. Accordingly, it is estimated that a considerable proportion of P _ky of 2θ = 40 degrees to 50 degrees is a component of P _d111 attributed to the (111) plane of the diamond crystal.

When Al ₄ C ₃ is used as the metal carbide, the intensity I _{10 at} 2θ = 10 degrees is about 8 times the intensity I _k of the peak at 2θ = 40 degrees to 50 degrees. When TiC is used as the metal carbide, the intensity I _{10 at} 2θ = 10 degrees is about four times the intensity I _k of the peak at 2θ = 40 degrees to 50 degrees. When SiC is used as the metal carbide, the intensity I _{10 at} 2θ = 10 degrees is about 10 times the intensity I _k of the peak at 2θ = 40 degrees to 50 degrees, and therefore SiC is used as the metal carbide. Moreover, it can be said that the pores of the porous carbon material are most developed.

FIG. 14 is an enlarged view of the portion of 2θ = 40 degrees to 50 degrees in FIG. It can be clearly seen that the porous carbon material produced by reacting SiC with chlorine gas at 1100 ° C. has a peak position on the highest angle side and exceeds 2θ = 43 degrees. Therefore, when the porous carbon material using SiC as the metal carbide contains Al ₄ C ₃ as the metal carbide or the porous carbon material using TiC as the metal carbide, it contains the most diamond component. I can say that.

Next, the heating temperature when reacting the metal carbide with chlorine gas will be described.
First, FIG. 4 shows the relationship between the heating temperature (treatment temperature) when silicon carbide is reacted with chlorine gas and the weight reduction rate of the metal carbide. The reaction formula between silicon carbide and chlorine gas is as follows.

SiC + 2Cl ₂ → SiCl ₄ + C

Since the molecular weight of SiC is about 40 and the atomic weight of carbon is 12, when the reaction proceeds 100%, the mass of the raw material SiC decreases by about 70%. Here, referring to FIG. 4, it is understood that the reaction proceeds almost 100% when silicon carbide is heated at 1000 ° C. for 4 hours or more in an atmosphere containing chlorine gas, regardless of the particle diameter of SiC as a raw material. it can. However, the chlorine gas concentration in the atmosphere containing chlorine gas is 9 mol%, and the balance is nitrogen gas.

As described above, when SiC is used as a raw material, a heating temperature of 1000 ° C. or lower is sufficient as long as the chlorination reaction only proceeds. On the other hand, by setting the heating temperature to 1100 ° C. or higher, a porous carbon material having a peak: P _{d111 in} which an X-ray diffraction image by CuKα rays belongs to the (111) plane of the diamond crystal is generated.

FIG. 5 shows the relationship between the heating temperature (Temp.) When silicon carbide is reacted with chlorine gas and the specific surface area (specific surface area) of the porous carbon material to be produced by the BET method and the Langmuir method. Shown for -plot. According to FIG. 5, it is shown that a reaction temperature of about 900 ° C. is sufficient if only the purpose is to obtain a porous carbon material having a large specific surface area. Moreover, it can be understood that the specific surface area tends to decrease somewhat as the heating temperature increases.

Further, FIG. 6 shows the relationship between the heating temperature when silicon carbide is reacted with chlorine gas and the pore size distribution (frequency-pore width characteristic diagram) of the porous carbon material to be produced. According to FIG. 6, as the heating temperature increases, the distribution peak position slightly shifts in the direction in which the pore diameter increases.
This corresponds to the fact that the specific surface area tends to decrease as the heating temperature increases.

On the other hand, FIG. 7 shows the relationship between the total pore volume (g / cc = g / cm ³ ) and the BET specific surface area of a porous carbon material produced by reacting silicon carbide with chlorine gas. FIG. 7 shows that the larger the BET specific surface area, the larger the total pore volume. Since the porous carbon material has a larger BET specific surface area and a larger pore volume, the porous carbon material is more suitable as an electrode active material for capacitors. Therefore, the heating temperature when chlorinating a metal carbide does not significantly reduce the BET specific surface area. It is preferable to set the temperature (for example, 1400 ° C. or lower).

FIG. 8 shows X-ray diffraction images of porous carbon materials produced by reacting silicon carbide and chlorine gas at 1100 ° C., 1200 ° C., and 1400 ° C. so that they can be compared with each other. FIG. 8 shows that any of the porous carbon materials produced at 1100 ° C. to 1400 ° C. does not have a peak attributed to the (002) plane of graphite: _PG002 and is on the (111) plane of the diamond crystal. It shows having an _assigned peak: _Pd111 . However, there is a tendency that the strength I _{d111 of} P _d111 increases as the heating temperature increases. This corresponds to the fact that when the heating temperature is too high, the size of the carbon microcrystal tends to increase.

Also in the X-ray diffraction image of FIG. 8, the intensity I _{10 at} 2θ = 10 degrees of the porous carbon material produced by reacting silicon carbide and chlorine gas at 1100 ° C., 1200 ° C. and 1400 ° C. is Compared to the peak intensity I _k of 2θ = 40 degrees to 50 degrees, it is 10 times or more.

[Capacitor]
Next, a capacitor including the porous carbon material as an electrode active material will be described.
Said porous carbon material is suitable as an electrode active material of an electric double layer capacitor (EDLC) or a lithium ion capacitor (LIC), for example. Therefore, although EDLC and LIC are demonstrated below, the kind of capacitor which can apply said porous carbon material is not specifically limited.

[Electric double layer capacitor (EDLC)]
The EDLC includes a first electrode, a second electrode, a separator interposed between the first electrode and the second electrode, and an electrolytic solution. Here, at least one of the first electrode and the second electrode includes the porous carbon material as an electrode active material for a capacitor. In EDLC, the first electrode and the second electrode generally have the same configuration.

[Lithium ion capacitor (LIC)]
The LIC includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive non-aqueous electrolyte. Here, at least one of the positive electrode and the negative electrode includes the porous carbon material as a positive electrode active material or a negative electrode active material. In the LIC, the positive electrode and the negative electrode generally have different configurations. For example, the porous carbon material described above is used for the positive electrode active material, and a material that can occlude and release lithium ions, a material that can be alloyed with lithium ions, or the like is used for the negative electrode active material.

[Capacitor electrode]
The electrode includes an electrode active material and an electrode current collector that holds the electrode active material.
The electrode current collector may be a metal foil, but is preferably a metal porous body having a three-dimensional network structure from the viewpoint of obtaining a high-capacity capacitor. The material of the metal porous body used for the positive electrode of LIC or the polarizable electrode of EDLC is preferably aluminum, aluminum alloy or the like.
On the other hand, the material of the metal porous body used for the negative electrode of LIC is preferably copper, copper alloy, nickel, nickel alloy, stainless steel or the like.

In the electrode for a capacitor, a slurry containing an electrode active material (porous carbon material) is applied to or filled in an electrode current collector, and then the dispersion medium contained in the slurry is removed. It is obtained by rolling a current collector that holds The slurry may contain a binder and a conductive additive in addition to the electrode active material. As the dispersion medium, for example, N-methyl-2-pyrrolidone (NMP), water or the like is used.

The type of the binder is not particularly limited, and for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like can be used. The amount of the binder is not particularly limited, but is, for example, 0.5 to 10 parts by mass per 100 parts by mass of the electrode active material.

The type of conductive aid is not particularly limited, and examples thereof include acetylene black, ketjen black, and carbon fiber. The amount of the conductive auxiliary agent is not particularly limited, but is, for example, 0.1 to 10 parts by mass per 100 parts by mass of the electrode active material.

As the electrode active material for capacitors, activated carbon is generally used, and activated carbon has been subjected to activation treatment. As the activation treatment, a gas activation method and a chemical activation method are generally used. The gas activation method is a treatment in which a carbon material is brought into contact with water vapor, carbon dioxide gas, oxygen or the like at a high temperature. The chemical activation method is a treatment in which a carbon material is impregnated with an activation chemical and heated in an inert gas atmosphere.
As the activation chemical, potassium hydroxide or the like is used. Therefore, activated carbon contains many impurities. On the other hand, the porous carbon material produced by chlorination of metal carbide hardly contains impurities as already described.

As the negative electrode active material of LIC, lithium titanium oxide, silicon oxide, silicon alloy, tin oxide, tin alloy, graphite, etc. can be used in addition to the porous carbon material.

It is preferable that the negative electrode active material of LIC is previously doped with lithium in order to lower the negative electrode potential. This increases the voltage of the capacitor, which is further advantageous for increasing the capacity of the LIC. The doping of lithium is performed when the capacitor is assembled. For example, lithium metal is accommodated in a capacitor container together with a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the assembled capacitor is kept warm in a constant temperature room at around 60 ° C., so that lithium ions are eluted from the lithium metal foil. Occluded by the active material. The amount of lithium doped into the negative electrode active material is preferably such that 5% to 90%, more preferably 10% to 75% of the negative electrode capacity (Cn) is filled with lithium. As a result, the negative electrode potential becomes sufficiently low, and it becomes easy to obtain a high-voltage capacitor.

The electrolytic solution of the capacitor contains a cation and an anion.
Examples of the cation include lithium ion (Li ⁺ ), tetraalkylphosphonium ion, tetraalkylammonium ion (for example, tetraethylammonium ion (TEA ⁺ ), triethylmonomethylammonium ion (TEMA ⁺ )), heterocyclic compound ion (imidazolium skeleton, imidazole) Use of ions having a linium skeleton, a pyridinium skeleton, a pyrrolidinium skeleton, or the like (eg, 1-ethyl-3-methylimidazolium ion (EMI ⁺ ), N-methyl-N-propylpyrrolidinium ion (MPPY ⁺ ))) Is preferred. These may be used alone or in combination of two or more. In addition, it is preferable that the alkyl group contained in ammonium ion etc. is C4 or less group.

As anions, hexafluorophosphate ions (PF ₆ ⁻ ), perchlorate ions (ClO ₄ ⁻ ), tetrafluoroborate ions (BF ₄ ⁻ ), lithium bis (oxalate) borate ions (BC ₄ O ₈₎ ^-), bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ^-), bis (trifluoromethanesulfonyl) imide ion (N (SO ₂ CF _{3) 2} ^-), bis (pentafluoroethane sulfonyl) imide ion (N ( SO ₂ C ₂ F ₅ ) ₂ ⁻ ), trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ) and the like are preferably used. These may be used alone or in combination of two or more.

The electrolytic solution used for EDLC may be an alkaline electrolytic solution or a nonaqueous electrolytic solution. Examples of the alkaline electrolyte include alkaline aqueous solutions such as a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution. As the non-aqueous electrolyte, for example, a non-aqueous solvent in which a salt of an onium ion (cation) selected from the above and a borate ion (anion) is dissolved is preferably used. The concentration of the salt in the nonaqueous electrolytic solution may be, for example, 0.3 mol / liter to 3 mol / liter.

The non-aqueous solvent used for EDLC is not particularly limited, and for example, sulfolane, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile and the like can be used. These may be used alone or in combination of two or more.

The onium ion used in EDLC is preferably a tetraalkylammonium ion or tetraalkylphosphonium ion having an alkyl group having 4 or less carbon atoms because it can impart excellent ionic conductivity to the electrolytic solution. Triethylmonomethylammonium ion (TEMA ⁺ ) Is particularly preferred. As the borate ion, tetrafluoroborate ion (BF ₄ ⁻ ) is preferable. Therefore, a specific example of a preferable salt is a salt of TEMA ⁺ and BF ₄ ⁻ (TEMA-BF ₄ ).

As the non-aqueous electrolyte used for LIC, a non-aqueous solvent in which a lithium salt is dissolved is preferably used. The concentration of the lithium salt in the nonaqueous electrolytic solution may be, for example, 0.3 mol / liter to 3 mol / liter. The lithium salt is not particularly limited, for _{example, LIClO 4, LiBF 4, LiPF} 6, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (pentafluoroethane sulfonyl) imide ion is preferably . These may be used alone or in combination of two or more.

The organic solvent used for LIC is not particularly limited, but from the viewpoint of ionic conductivity, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, formic acid Aliphatic carboxylates such as methyl, methyl acetate, methyl propionate and ethyl propionate, lactones such as γ-butyrolactone and γ-valerolactone, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetoa Mido, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, trimethoxymethane, sulfolane, methylsulfolane, 1,3-propane sultone and the like can be used.
These may be used alone or in combination of two or more.

An ionic liquid can also be used as a non-aqueous solvent used for LIC. An ionic liquid is a salt that is liquid at room temperature. For example, a salt of an onium ion (cation) selected from the above and an imide ion or sulfonate ion (anion) is preferably used as the ionic liquid. The onium ion is preferably an ion having an imidazolium skeleton, an imidazolinium skeleton, a pyridinium skeleton, a pyrrolidinium skeleton, or the like.

More specifically, the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium ion (EMI ⁺ ) and N-methyl-N-propylpyrrolidinium ion (MPPY ⁺ ) as the cation. Contains at least one kind, and anions include bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ⁻ ), bis (trifluoromethanesulfonyl) imide ion (N (SO ₂ CF ₃ ) ₂ ⁻ ), bis (pentafluoroethane It preferably contains at least one selected from the group consisting of (sulfonyl) imide ions (N (SO ₂ C ₂ F ₅ ) ₂ ⁻ ) and trifluoromethanesulfonate ions (CF ₃ SO ₃ ⁻ ). Among these, as the cation, 1-ethyl-3-methylimidazolium ion (EMI ⁺ ) is particularly preferable from the viewpoint of excellent ion conductivity. On the other hand, as the anion, bis (fluorosulfonyl) imide ion (FSI ⁻ ) and bis (trifluoromethanesulfonyl) imide ion (TFSI ⁻ ) are particularly preferable.

As a specific composition of the non-aqueous electrolyte using an ionic liquid, for example, a mixture of a salt of EMI ⁺ and FSI ⁻ (EMI-FSI) and lithium bis (fluorosulfonyl) imide (LiFSI) can be mentioned. . Such a composition is considered to be compatible with a porous carbon material obtained by chlorination of metal carbide. In the mixture of EMI-FSI and LiFSI, the LiFSI content is desirably 5 mol% to 30 mol%. By setting it as such a composition, it becomes advantageous for coexistence with the outstanding ionic conductivity and the permeability | transmittance to the electrode of electrolyte solution.

[Separator]
Between the pair of electrodes or between the positive electrode and the negative electrode, they can be physically separated to prevent a short circuit, and a separator having ion permeability can be interposed. The separator has a porous material structure and allows ions to permeate by holding the electrolytic solution in the pores. As a material for the separator, for example, polyolefin, polyethylene terephthalate, polyamide, polyimide, cellulose, glass fiber, or the like can be used.

FIG. 9 schematically shows a configuration of an example of a capacitor. In the cell case 45, an electrode plate group and an electrolytic solution which are main components of the capacitor 40 are accommodated. The electrode plate group is configured by laminating a plurality of first electrodes (positive electrodes) 41 and second electrodes (negative electrodes) 42 via separators 43. The first electrode 41 includes a first electrode current collector 41a having a three-dimensional network structure, and a particulate first electrode active material 41b filled in a communication hole of the first electrode current collector 41a. ing. The second electrode 42 includes a second electrode current collector 42a having a three-dimensional network structure, and a particulate second electrode active material 42b filled in a communication hole of the second electrode current collector 42a. ing.
However, the electrode plate group is not limited to the laminated type, and can be configured by winding the first electrode 41 and the second electrode 42 via the separator 43.

In the case where the capacitor 40 is a LIC, it is desirable to make the size of the negative electrode 42 larger than that of the positive electrode 41 as shown in FIG. 9 from the viewpoint of preventing lithium from being deposited on the negative electrode 42.

Next, an example of the industrial manufacturing method of a porous carbon material is demonstrated in detail.
The porous carbon material includes, for example, (i) a step of generating a porous carbon material and a first metal chloride by heating the first metal carbide in an atmosphere containing chlorine gas; Reducing the first metal chloride by reacting with the second metal to produce the first metal and the second metal chloride; and (iii) reacting the first metal with carbon to produce the first metal chloride. Producing efficiently on an industrial scale by a production method comprising a step of producing a metal carbide and (iv) a step of producing a second metal and chlorine gas by reducing the second metal chloride. Can do. In addition, the order of process (iii) and process (iv) is not specifically limited, Which may be performed first and both processes may be performed in parallel.

In the above manufacturing method, in step (i), the first metal carbide (SiC, TiC, etc.) reacts with chlorine gas (Cl ₂ ), and the porous carbon material and the first metal chloride (SiCl ₄ , TiCl _4, etc.) are reacted. ) And generate. The produced first metal chloride is reduced in step (ii) and taken out as the first metal (Si, Ti, etc.). The extracted first metal is carbonized in step (iii), and the first metal carbide (SiC, TiC, etc.) is regenerated. The regenerated first metal carbide is reused in step (i). In step (ii), a second metal chloride (ZnCl ₂ , MgCl _2, etc.) is generated. The produced second metal chloride is reduced in step (iv), and the second metal (Zn, Mg, etc.) and chlorine gas (Cl ₂ ) are regenerated. The regenerated second metal is reused in the step (ii), and the regenerated chlorine gas is reused in the step (i). As described above, all materials other than carbon used in step (iii) are reused. Therefore, according to the manufacturing method, the environmental load is low and the production cost can be suppressed.

The first metal carbide to be reacted with chlorine gas is, for example, a powder or a porous body. Thereby, a porous carbon material can be efficiently taken out from the first metal carbide.

As the first metal carbide, for example, at least one selected from the group consisting of SiC and TiC can be used. However, it is considered that SiC is most preferable as a raw material for the porous carbon material having an X-ray diffraction image having a peak attributed to the (111) plane of diamond. On the other hand, other metal carbides may be used as long as a porous carbon material exhibiting a desired X-ray diffraction image can be generated by improving the manufacturing conditions. Examples of other metal carbides include Al ₄ C ₃ , ThC ₂ , B ₄ C, CaC ₂ , Cr ₃ C ₂ , Fe ₃ C, UC ₂ , WC, and MoC. These may be used alone or in combination of two or more.

The atmosphere containing chlorine gas may be an atmosphere containing only chlorine gas, or a mixed gas atmosphere of chlorine gas and inert gas. Thereby, while being able to improve the safety of the manufacturing equipment which performs process (i), degradation of manufacturing equipment can be controlled.

As described above, the heating temperature for reacting the first metal carbide and chlorine gas is preferably 1100 ° C. or more and 1500 ° C. or less, and more preferably 1100 ° C. to 1400 ° C., for example. Thereby, the reaction efficiency between the first metal carbide and the chlorine gas can be increased, and a porous carbon material having a desired X-ray diffraction image and a large specific surface area can be efficiently obtained.

As the second metal, for example, at least one selected from the group consisting of Group 1 elements, Group 2 elements, Group 11 elements and Group 12 elements can be used. Thereby, the reduction reaction of a 1st metal chloride can be advanced efficiently.

Hereinafter, the details of the method for producing the porous carbon material will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

FIG. 10 is a flowchart showing the flow of each step of an example of the method for producing the porous carbon material. Here, the case where SiC is used as the first metal carbide and zinc (Zn) is used as the second metal is shown. As shown in FIG. 10, the present manufacturing method includes a step (i) (S11) of generating a porous carbon material, a step (ii) (S12) of reducing the first metal chloride, and the first metal carbide. (Iii) (S13), and (iv) (S14) for reducing the second metal chloride, and these steps are repeated. Thereby, the porous carbon material derived from SiC can be continuously produced.

Step (i) is a step in which the first metal carbide and chlorine gas are brought into contact with each other and heat-treated. In this step, only the first metal contained in the crystal of the first metal carbide reacts with the chlorine gas, and only the first metal escapes from the crystal, forming a porous carbon. This step is performed in an atmosphere containing chlorine gas. The atmosphere containing chlorine gas may be a substantially 100% chlorine gas atmosphere, but may also be a mixed gas atmosphere of chlorine gas and an inert gas (N ₂ , He, Ar, Ne, Xe, etc.). The mixing ratio of chlorine gas and inert gas (chlorine gas: inert gas) is preferably 1:50 to 1: 1 in terms of flow rate.

In step (i), a first metal chloride (such as SiCl ₄ ) is obtained together with the porous carbon material. The first metal chloride is cooled to below the boiling point of the chloride with a cooler or the like, and then recovered.

In step (i), it is preferable to use powdered or porous metal carbide. This is because the first metal located deeper from the surface of the metal carbide requires a longer time to escape as chloride. By using a powdered or porous metal carbide having a large surface area, the first metal can efficiently escape from the metal carbide. Therefore, the manufacturing time of the porous carbon material can be shortened. The average particle size of the metal carbide is preferably 0.1 μm to 100 μm, and more preferably 2 μm to 40 μm. By adjusting the metal carbide to such an average particle diameter in advance, it becomes easy to obtain a porous carbon material having a sharper distribution and a large total pore volume per unit mass. It is also effective to use raw materials having several kinds of average particle diameters in order to increase the packing density of the powder.

After step (i), the first metal chloride is reduced (step (ii)). As the reducing agent, a second metal that is more easily oxidized than the first metal is used. Thereby, a highly purified 1st metal can be taken out from a 1st metal chloride. Group 2 elements include Group 1 elements (Group 1A elements, alkali metals), Group 2 elements (Group 2A elements, alkaline earth metals), Group 11 elements (Group 1B elements) such as Cu, Zn It is preferable to use a Group 12 element (Group 2B element) or the like. These may be used alone or in combination of two or more. Among these, Zn is desirable in that the melting point of chloride is relatively low and the vapor pressure is high. That is, as the step (ii), it is preferable to employ a so-called zinc reduction method. In addition to Zn, Mg, Na, K, Sr, Ba, Ca and the like are also suitable as the second metal.

Next, the carbonization reaction of the first metal produced in step (ii) (step (iii)) and the reduction reaction of the second metal chloride (step (iv)) are performed. In step (iii), the metal carbide is regenerated by reacting the first metal with carbon. Here, as a carbon raw material used for carbonization, low-cost and easily available materials such as carbon black and natural graphite can be used. The regenerated metal carbide is reused in step (i).

In step (iv), the second metal and chlorine gas are extracted by electrolysis of the second metal chloride. Specifically, the second metal chloride is separated into the second metal and chlorine gas by electrolyzing the second metal chloride in a high-temperature molten state. The extracted chlorine gas is reused in step (i). Further, the extracted second metal is reused in the step (ii).

Next, an example of a carbon production apparatus that generates a porous carbon material will be described. FIG. 11 schematically shows the configuration of the carbon generator 10. Moreover, in FIG. 12, the structure of the zinc reduction apparatus 20 used by process (ii) and process (iv) is simplified and shown. Furthermore, in FIG. 13, the structure of the carbide | carbonized_material production | generation apparatus 30 used by process (iii) is shown roughly.

Referring to FIG. 11, the carbon generator 10 includes a reaction furnace 11, a cooling trap 12, and a storage tank 13. The reaction furnace 11 accommodates a mounting shelf 11a for mounting metal carbides over a plurality of stages. The mounting shelf 11a is supported by being suspended from above by a support bar 11b. A gas introduction port 11 c is provided in a portion of the reaction furnace 11 below the mounting shelf 11 a. A mixed gas of chlorine gas and inert gas or substantially 100% chlorine gas is introduced into the reaction furnace 11 from the gas inlet 11c. A heater 11d is provided outside the reaction furnace 11 so as to surround the mounting shelf 11a. The mixed gas or chlorine gas around the metal carbide is heated by the heater 11d so as to have a predetermined temperature of 1100 ° C. or higher and 1500 ° C. or lower.

In the reaction furnace 11, the first metal is released from the metal carbide, and a porous carbon material is generated on the mounting shelf 11a. Further, the first metal chloride and the mixed gas (or chlorine gas) generated by the reaction are discharged to the outside of the reaction furnace 11 from a gas discharge port 11 e provided in the upper part of the reaction furnace 11. The gas discharge port 11 e is connected to the cooling trap 12, and the exhaust from the reaction furnace 11 is cooled by the refrigerant 12 a circulating in the cooling trap 12. Then, the cooled first metal chloride is stored in the storage tank 13 and then sent to the zinc reduction device 20. On the other hand, the mixed gas (or chlorine gas) that has passed through the cooling trap 12 is exhausted to the outside of the carbon generator 10 through the three-way valve 14 or is sent again to the gas inlet 11 c of the reaction furnace 11.

Referring to FIG. 12, the zinc reduction device 20 includes vaporizers 21 and 22, a reaction furnace 23, and a molten salt electrolyzer 24. The first metal chloride stored in the storage tank 13 of the carbon generator 10 is sent to the vaporizer 21 and vaporized. On the other hand, in the vaporizer 22, the second metal is vaporized. The first metal chloride and the second metal thus vaporized are sent to the reaction furnace 23. Then, in the reaction furnace 23, the first metal chloride and the second metal are reacted at a high temperature, whereby the first metal is taken out and the second metal chloride is generated. The second metal chloride is sent to the molten salt electrolytic cell 24 and separated into the second metal and chlorine gas by electrolysis. The chlorine gas thus taken out is sent to the carbon generator 10, and the second metal is sent to the vaporizer 22.

Subsequently, referring to FIG. 13, the carbide generating device 30 includes a reaction furnace 31 extending in the vertical direction, a heater 32 embedded in the side wall of the reaction furnace 31, and a mounting shelf 33 disposed in the reaction furnace 31. It has. On the mounting shelf 33, a mixture 34 of the first metal and the carbon raw material (carbon black or natural graphite) is mounted in a plurality of stages. The mounting shelf 33 is supported by being suspended from above by a support bar 33a.

An intake port 31a is provided in the lower part of the reaction furnace 31, and an inert gas (N ₂ , He, Ar, Ne, Xe, etc.) is introduced from the intake port 31a. The inert gas moves upward in the reaction furnace 31 and is then discharged from an exhaust port 31 b provided in the upper part of the reaction furnace 31.

The heater 32 is disposed so as to surround the periphery of the mounting shelf 33, and heats the mixture 34 mounted on the mounting shelf 33. A suitable temperature of the mixture 34 in this step is 1400 ° C. to 1800 ° C. Thereby, a 1st metal and carbon couple | bond together and a metal carbide is reproduced | regenerated.

In the above manufacturing method and manufacturing apparatus, all materials other than the carbon raw material used for generating the porous carbon material are circulated and reused. Therefore, it is clear that the environmental load can be reduced and the production cost can be suppressed.

Example 1
(I) Synthesis of SiC Reaction in which a mixture of activated carbon (average particle size 20 μm, specific surface area 80 m ² / g) and silicon particles (average particle size 100 μm) was placed on a carbon mounting shelf and set to 900 ° C. A mounting shelf was inserted into the nitrogen gas atmosphere in the furnace. Thereafter, the temperature in the reaction furnace was raised to 1450 ° C. at a temperature rising rate of 10 ° C./min to melt silicon, and in this state, activated carbon and silicon were reacted for 5 hours. The product obtained was beta-type SiC. The obtained SiC was pulverized until the average particle size became 10 μm.

(Ii) Production of porous carbon material SiC having an average particle size of 10 μm was placed on a carbon mounting shelf of an electric furnace having a quartz glass furnace core tube. Then, chlorine gas was circulated at a flow rate of 1000 ml / min and Ar gas was flowed at a flow rate of 5000 ml / min in the electric furnace, and SiC and chlorine gas were reacted at 1100 ° C. for 2 hours. At this time, a cooling trap set at −20 ° C. was provided at the exhaust port of the core tube, and SiCl ₄ was liquefied and collected by the cooling trap. Further, chlorine gas that did not react with SiC in the core tube was refluxed to the core tube by a three-way valve installed on the outlet side of the cooling trap. Thereafter, the chlorine gas in the furnace core tube was removed by Ar gas, the temperature of the carbon mounting shelf was lowered to 400 ° C., and the porous carbon material remaining on the mounting shelf was taken out into the atmosphere.

(Iii) Physical property evaluation of porous carbon material (a) XRD
When an X-ray diffraction image of the porous carbon material by Cuka radiation was measured, a diffraction image as shown in FIG. 1 was obtained. No peak attributed to the (002) plane of graphite was observed at 2θ = 20 to 30 degrees (I _G002 / I _k = 0). On the other hand, a broad peak _Pd111 attributed to the (111) plane of diamond was observed at 2θ = 40 ° to 50 °. The crystallite size determined from the half width of P _d111 using the Scherrer equation was 2.0 nm.

(B) Electron microscope observation After the cross section of the porous carbon material was polished, it was observed with a high-resolution TEM. As a result, as shown in FIG. 2, the presence of microcrystals having an onion structure with a diameter of about 2 nm was confirmed.

(C) Pore size distribution The pore size distribution of the porous carbon material was determined by isothermal adsorption of N ₂ at −196 ° C. (using BELLSORP-miniII manufactured by Bell Japan). As shown in FIG. A sharp distribution with a peak at 0.32 nm was obtained. The cumulative volume of pores having a pore diameter of 1 nm or less was 90% of the total pore volume.

(D) Impurity concentration When the composition of the porous carbon material was analyzed by the inductively coupled plasma method, no transition metal element and alkali metal element were detected as impurities (the detection limit of analysis was 10 ppm). Moreover, when the desorption amount of the hydrogen component was measured with a gas chromatograph mass spectrometer while raising the temperature to 800 ° C., the hydrogen content was 50 ppm.

(E) BET specific surface area The BET specific surface area of the porous carbon material was measured by N ₂ isothermal adsorption measurement (BELLSORP-mini II manufactured by Bell Japan), and was 1250 m ² / g.

(Iv) Production of Capacitor Electrode An aluminum porous body having an average cell diameter of 550 μm, a basis weight of 150 g / m ² and a thickness of 1000 μm was prepared as an electrode current collector. On the other hand, 100 parts by mass of the porous carbon material (average particle size of about 10 μm), 2 parts by mass of ketjen black as a conductive additive, 4 parts by mass of polyvinylidene fluoride powder as a binder, and N-methyl-2- An electrode slurry was prepared by adding 15 parts by mass of pyrrolidone (NMP) and stirring with a mixer. The obtained slurry was filled into a current collector, dried, and rolled with a roller to obtain an electrode having a thickness of 480 μm.

(V) Preparation of Electrolytic Solution TEMA-BF ₄ was dissolved at a concentration of 1.5 mol / L in propylene carbonate, which is a nonaqueous solvent, and used as an electrolytic solution.

(Vi) Production of Cell A plate group was formed by interposing a cellulose separator having a thickness of 60 μm between a pair of electrodes. Thereafter, the electrode group and the electrolytic solution were accommodated in an aluminum laminate bag, and an EDLC having a nominal capacitance of 10F was completed.

[Capacitor evaluation]
With respect to the obtained EDLC, when the voltage range was 0.0 V to 3.6 V and the capacity per 1 g of the porous carbon material was determined, it was 50 F / g.

Next, after repeating the charge / discharge cycle 5000 times, the capacity retention rate with respect to the initial capacity was examined and found to be 98%.

Example 2
A porous carbon material was produced in the same manner as in Example 1 except that TiC was used instead of SiC. The X-ray diffraction image of the obtained porous carbon material had a broad peak attributed to the (002) plane of graphite at 2θ = 20 ° to 30 ° as shown by the waveform Y in FIG. . On the other hand, a broad peak: P _k was also observed at 2θ = 40 ° to 50 °. Here, I _G002 / I _k is 2.7, and it is assumed that most of P _k is a component of P _d111 . The crystallite size obtained from the half width of P _k using the Scherrer equation was 1.9 nm.

When the pore diameter distribution of the porous carbon material was determined in the same manner as in Example 1, a sharp distribution having a peak at 0.4 nm was obtained. The cumulative volume of pores having a pore diameter of 1 nm or less was 93% of the total pore volume. Further, when the composition of the porous carbon material was analyzed by inductively coupled plasma optical emission spectrometry, no transition metal element and alkali metal element were detected as impurities. The hydrogen content was 10 ppm. Furthermore, when the BET specific surface area of the porous carbon material was measured in the same manner as in Example 1, it was 1500 m ² / g.

When the capacitor of Example 2 was evaluated in the same manner as in Example 1, the capacity per gram of activated carbon was 51 F / g, and the capacity retention rate was 97%.

<< Comparative Example 1 >>
A capacitor was produced in the same manner as in Example 1 except that activated carbon having a BET specific surface area of 2100 m ² / g and an average particle size of 10 μm was used instead of the SiC-derived porous carbon material used in Example 1. When the pore size distribution of the activated carbon was measured, a peak was observed at 1.9 nm.

When the capacitor of Comparative Example 1 was evaluated in the same manner as in Example 1, the capacity per 1 g of activated carbon was 30 F / g, and the capacity retention rate was 93%.

<< Comparative Example 2 >>
A capacitor was produced in the same manner as in Example 1 except that carbon nanotubes (CNT) having a BET specific surface area of 600 m ² / g were used instead of the SiC-derived porous carbon material used in Example 1.

When the capacitor of Comparative Example 2 was evaluated in the same manner as in Example 1, the capacity per 1 g of CNT was 2 F / g, and the capacity retention rate was 94%.

<< Comparative Example 3 >>
A porous carbon material was produced in the same manner as in Example 1 except that Al ₄ C ₃ was used instead of SiC. The X-ray diffraction image of the obtained porous carbon material had a peak attributed to the (002) plane of graphite at 2θ = 20 ° to 30 ° as shown by the waveform Z in FIG. On the other hand, a broad peak: P _k was observed at 2θ = 40 ° to 50 °. Here, I _G002 / I _k is 4.3, and P _k is presumed to contain virtually no component of P _d111 .

When the pore diameter distribution of the porous carbon material was determined in the same manner as in Example 1, a sharp distribution having a peak at 1.5 nm was obtained. The cumulative volume of pores having a pore diameter of 1 nm or less was 55% of the total pore volume. Further, when the composition of the porous carbon material was analyzed by inductively coupled plasma atomic emission spectrometry, no transition metal element and alkali metal element were detected as impurities. Furthermore, when the BET specific surface area of the porous carbon material was measured in the same manner as in Example 1, it was 1120 m ² / g.

When the capacitor of Comparative Example 3 was evaluated in the same manner as in Example 1, the capacity per 1 g of the porous carbon material was 36 F / g, and the capacity retention rate was 92%.

The capacitor electrode active material of the present invention can be used for various capacitors such as EDLC and LIC. The capacitor of the present invention is promising as a power source for, for example, an electric vehicle and a hybrid vehicle because of its low electric resistance and excellent cycle characteristics.

DESCRIPTION OF SYMBOLS 10 ... Carbon generator, 11 ... Reactor, 12 ... Cooling trap, 13 ... Storage tank, 14 ... Three-way valve, 20 ... Zinc reduction device, 21, 22 ... Vaporizer, 23 ... Reactor, 24 ... Molten salt electrolyzer 30 ... Carbide generator, 31 ... Reactor, 32 ... Heater, 33 ... Mounting shelf, 34 ... Mixture, 40 ... Capacitor, 41 ... First electrode (positive electrode), 42 ... Second electrode (negative electrode), 43 ... Separator, 45 ... Cell case

Claims (12)

1. Including porous carbon material,
   The BET specific surface area of the porous carbon material is 800 m ² / g or more,
   An X-ray diffraction image of the porous carbon material by Cukα rays has a peak: P _k at 2θ = 40 ° to 50 °, and P _k is a peak attributed to the (111) plane of the diamond crystal: P _d111 Of ingredients,
   The peak X-ray diffraction pattern is attributed to the (002) plane of the graphite: if it has a P _G002, the strength of P _G002: intensity of P _k of I _G002: ratio I _k (I _G002 / I _k ) Is 3.0 or less, an electrode active material for capacitors.
2. The capacitor active material according to claim 1, wherein the position of P _k is on a higher angle side than 2θ = 43 degrees.
3. 3. The capacitor active material according to claim 1, wherein the strength of P _k is three times or more of the strength of 2θ = 10 degrees.
4. The capacitor electrode active material according to any one of claims 1 to 3, wherein a crystallite size obtained from a half-value width of P _k is 1.0 nm to 10.0 nm.
5. The integrated volume of pores having a pore diameter of 1 nm or less in the volume-based pore diameter distribution of the porous carbon material is 80% or more of the total pore volume, and any one of claims 1 to 4. The electrode active material for capacitors according to Item.
6. 6. The electrode active material for a capacitor according to claim 1, wherein the content of the alkali metal element in the porous carbon material is 0 ppm to 400 ppm.
7. The capacitor electrode active material according to any one of claims 1 to 6, wherein the hydrogen content of the porous carbon material is 0 ppm to 100 ppm.
8. A first electrode, a second electrode, a separator interposed between the first electrode and the second electrode, and an electrolytic solution,
   A capacitor, wherein at least one of the first electrode and the second electrode includes the electrode active material for a capacitor according to any one of claims 1 to 7.
9. The electrolyte includes, as cations, lithium ion (Li ⁺ ), tetraethylammonium ion (TEA ⁺ ), triethylmonomethylammonium ion (TEMA ⁺ ), 1-ethyl-3-methylimidazolium ion (EMI ⁺ ), and N-methyl. Including at least one selected from the group consisting of —N-propylpyrrolidinium ion (MPPY ⁺ ), and as anions, hexafluorophosphate ion (PF ₆ ⁻ ), perchlorate ion (ClO ₄ ⁻ ), tetra Fluoroborate ion (BF ₄ ⁻ ), lithium bis (oxalate) borate ion (BC ₄ O ₈ ⁻ ), bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ⁻ ), bis (trifluoromethanesulfonyl) imide ion ( N (SO ₂ CF ₃ ) ₂ ⁻ ), bis (pentafluoroethane The capacitor according to claim 8, comprising at least one selected from the group consisting of (sulfonyl) imide ion (N (SO ₂ C ₂ F ₅ ) ₂ ⁻ ) and trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ).
10. A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive non-aqueous electrolyte,
    A lithium ion capacitor in which at least one of the positive electrode and the negative electrode contains the electrode active material for a capacitor according to any one of claims 1 to 7.
11. The lithium ion capacitor according to claim 10, wherein the nonaqueous electrolytic solution includes a nonaqueous solvent and a lithium salt that dissolves in the nonaqueous solvent, and the nonaqueous solvent is an ionic liquid or an organic solvent. .
12. The ionic liquid contains at least one selected from the group consisting of 1-ethyl-3-methylimidazolium ion (EMI ⁺ ) and N-methyl-N-propylpyrrolidinium ion (MPPY ⁺ ) as a cation. As anions, bis (fluorosulfonyl) imide ion (N (SO ₂ F) ₂ ⁻ ), bis (trifluoromethanesulfonyl) imide ion (N (SO ₂ CF ₃ ) ₂ ⁻ , bis (pentafluoroethanesulfonyl) imide ion (N The lithium ion capacitor according to claim 11, comprising at least one selected from the group consisting of (SO ₂ C ₂ F ₅ ) ₂ ⁻ ) and trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ).

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